The Applicant of the present application has marketed a portable lamp, of the type headlamp, with a so-called “reactive” or “dynamic” lighting which is described in patent application WO2009/133309. Briefly, as illustrated in prior art FIG. 1, there is a headlamp having at least one light emitting diode 15 and a LED type optical sensor 14 located in the vicinity and for sensing a signal representative of the light reflected by the surface of an object illuminated by the lamp 16. A control circuit 13 processes the signal for the purpose of automatically controlling the power of the LED according to a predetermined threshold. In this way, an automatic adjustment of the light beam emitted by the lamp can be achieved without any manual action to adapt the light to the environment, while managing energy consumption.
The principle of this light “dynamic” is clearly a significant improvement brought in field of headlamps, and more generally portable lighting.
However, despite the significant advantages which are therefrom resulting, such headlamp has shown new problems.
Indeed, a high sensitivity of the control system to the disturbing light sources actually has been actually observed.
For example if the user illuminates a scene in the distance and an object—even a small one—causes a reflected portion of the light produced by the lamp to interfere with the control system, the latter might be disturbed and causes a reduction of the light emission power, even if it is not required nor desirable.
In a second example, one has noticed a disturbance in the light regulation when the holder of the lamp is walking on a road and comes to cross the lights of a vehicle traveling in the opposite direction. In this case, as previously, the control system is spoiled by the interfering light produced by the vehicle lights and once again inappropriately reduce the brightness of the lamp.
Finally, one can also evoke a third example—that of a climber on the rope—whose dynamic lighting might be disturbed by the rope moving right and left in front of the photosensor.
A solution to this problem is described in two patent applications PCT/EP2012/000982 and PCT/EP2012/000984, both filed Mar. 6, 2012 by the assignee of this patent application and unpublished at the time of filing this application. This solution requires the use of an image sensor associated to a image process which can process images so as to allow a more sophisticated control, either of the brightness of the LEDs or of the geometry of the light beam.
Those solutions however require a more sophisticated architecture which significantly increases the manufacturing costs of those headlamps.